linux-kernel - Re: [PATCH v4 2/3] mm: introduce put_user

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 10 Oct 2018 16:45:41 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     <john.hubbard@...il.com>, Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Christopher Lameter <cl@...ux.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dan Williams <dan.j.williams@...el.com>,
        Jan Kara <jack@...e.cz>, <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, Al Viro <viro@...iv.linux.org.uk>,
        Jerome Glisse <jglisse@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Ralph Campbell <rcampbell@...dia.com>
Subject: Re: [PATCH v4 2/3] mm: introduce put_user_page*(), placeholder
 versions

On Tue, 9 Oct 2018 17:42:09 -0700 John Hubbard <jhubbard@...dia.com> wrote:

> > Also, maintainability.  What happens if someone now uses put_page() by
> > mistake?  Kernel fails in some mysterious fashion?  How can we prevent
> > this from occurring as code evolves?  Is there a cheap way of detecting
> > this bug at runtime?
> > 
> 
> It might be possible to do a few run-time checks, such as "does page that came 
> back to put_user_page() have the correct flags?", but it's harder (without 
> having a dedicated page flag) to detect the other direction: "did someone page 
> in a get_user_pages page, to put_page?"
> 
> As Jan said in his reply, converting get_user_pages (and put_user_page) to 
> work with a new data type that wraps struct pages, would solve it, but that's
> an awfully large change. Still...given how much of a mess this can turn into 
> if it's wrong, I wonder if it's worth it--maybe? 

This is a real worry.  If someone uses a mistaken put_page() then how
will that bug manifest at runtime?  Under what set of circumstances
will the kernel trigger the bug?

(btw, please cc me on all patches, not just [0/n]!)